Spectroscopy has been used for years in research laboratories and in numerous chemical industries for identifying, measuring, monitoring, and controlling the development and the commercial production of new and existing chemicals, pharmaceuticals, foods, beverages, paints, plastics, semiconductors, and other chemically-based materials. The application of spectroscopy requires both instrumentation and numerical tools to resolve and quantify the chemical compounds which make up the composite spectral records when multicomponent systems are analyzed.
For many years, chemical spectroscopy in industrial settings was performed off-line from the process line, with samples being extracted and taken to an analytical laboratory for analysis and interpretation; this procedure often consumed hours or days before the results were reported back to the chemical process engineer or technician. As a consequence, if the analysis revealed that the chemical process had strayed for its design formulation, the final products could not be used and great quantities of material, time, and money were wasted. In more recent years, on-line instrumentation has been developed and applied to provide chemical analyses which are timely within tens of minutes or more; the result being significantly greater economies of operation and production and higher qualities of finished products. With each improvement achieved, however, process engineers and company executives demand even better systems and increased cost savings.
Every year the semiconductor industry increases the development and use of technology; this leads to added refinements in their production standards and quality levels. Among these changes, the semiconductor industry demands electronic specialty gases with increasingly higher levels of purity every year.
The presence of impurities such as moisture in etching gases can cause corrosion of gas handling systems. The corrosion in a gas handling system leads to the production of particles that can be transported by the high purity gas stream to the wafer. If the gas handling system is contaminated by corrosion particles, these particles can impact device yields or can even cause a process line failure. In both cases, the corroded gas handling system must be replaced. For example, a gas such as HCI containing moisture contamination levels as low as one part per million over volume (1 ppm/v) can cause this problem. Equally important, the variation in moisture impurity levels changes the kinetics of the chemical etching process by perturbing the time sequence for the etching stages. This can cause incorrect electronic circuitry to be generated in the silicon wafer, which can cause entire batches of wafers to be wasted.
Specialty gas manufacturers are required to perform a gas analysis for certification on every gas tank shipped to wafer fab plants. So every gas tank has to go from the production area to the analytical lab to be certified by qualified personnel. On the other hand, at the semiconductor facility, even though every gas tank has been certified, there is still the issue of gas contamination introduced by gas tank degradation over time and improper connection of the gas tank to the manifold system. Also, there is a concern for the presence of leaks between the gas tank and the etching tools when using sub-atmospheric pressure to transport the etching gases; so a final check at the semiconductor facility is also required, either at the gas tank supply point and/or at the process tool.
There are many tools in today""s market which provide manual off-line gas analysis and certification. But, to date, there does not exist an analytical tool assembled together, as a complete solution, available on the market that can provide on-line continuous analysis for low concentrations (below the 1 ppm/v level) of moisture and other impurities in the corrosive etching gases. However, as the system described in this thesis continues to develop, a system which meets these needs will soon be introduced to the market.
There are several techniques available to determine moisture concentration in gases, but not all of them are suitable for industrial applications such as on-line gas analysis. The following is a table (Table 1) of these techniques, including their pros and cons, for industrial application.
As shown in Table 1, FTIR Spectroscopy offers the best characteristics for an on-line, continuous gas analyzer. It offers not only the means of determining moisture concentrations in corrosive etching gases, but it is also suitable for detecting other destructive impurities which may be present in the gas at the same time. This method can be used not only with corrosive gases but also with all gases in general as well. So, the present inventions provides a real-time, on-line and continuous system that can detect traces of different impurities present in the corrosive etching gases.
This present invention provides an industrial turnkey system comprising an automatic on-line monitoring analytical tool for the detection of impurities in corrosive gases in real-time. The system is based on FTIR spectroscopy and controlled by software running on a personal computer. The software provides integration and control of the hardware elements, as well as the spectral analysis and chemometrics, to determine the concentration of impurities in gases. The system is not only capable of detection of low levels of impurities in real-time, but it also provides a method to minimize problems commonly associated with FTIR quantification analysis.
The present invention provides a 10-to-100-fold advancement in the time resolution available to process engineers for monitoring the quality of their real-time chemical process operations. This advancement is obtained by creating chemical spectroscopy quantification software which records, counts, and displays the dynamic impact of every single spectral scan, while at the same time producing data that are time-averages of multiple scans from any type of scanning spectrometer.
As a consequence, changes in an ongoing chemical process, whether undesired or desired, can be detected within the smallest resolvable time interval or period of a single scan of a given spectrometer. For example, using a FTIR spectrometer, the period of a single scan is typically a few seconds. So the effective time resolution for process monitoring becomes seconds rather than minutes.
The present invention achieves its enhancement in time resolution by means of the application of mathematical algorithms which manage and display the data associated with every single spectrometer scan. The invention is available either integrated with the chemical spectroscopy quantification software of the present invention or as a module which can be incorporated into existing commercial spectral analysis software.
The present invention is of a system and method for detection of impurities in gases comprising: providing a Fourier transform infrared spectrometer and employing computer apparatus comprising system control computation apparatus, spectral analysis computation apparatus, and chemometrics computation apparatus. A limit of detection of gas impurities of between approximately 10-25 ppb/v. is provided. In the preferred embodiment, the system control controls gas flow through a gas manifold using gas flow control computation apparatus, controls moisture buildup employing temperature control computation apparatus, and adjusts a transfer mirror. Signal-to-noise ratio is increased by alternating scans between background spectra and sample spectra. Chemometrics employs a running average of a plurality of scans, computes an average concentration of an impurity at every scan, and reports changes in impurity concentrations occurring from both scan to scan and over said plurality of scans. Errors resulting from baseline drift are reduced by assuming that system baseline is not necessarily centered around an x-axis of collected spectra.